1. Technical Field
The present invention relates to an apparatus and a method for controlling a vehicle.
2. Related Art
Japanese Unexamined Patent Application Publication No. H10-271613, for example, discloses a driving control apparatus for an electric vehicle that is capable of driving left and right rear wheels independently and which implements driving stability control which controls moment about the center of gravity of the vehicle based on a yaw rate. The driving control apparatus uses a yaw rate F/B value as a yaw rate sensor value.
In the case where the vehicle is driven with the yaw rate F/B value used as the yaw rate sensor value, if the condition of a road surface changes from a high μ condition to a low μ condition, a tire of the vehicle may slip when drive control assumes a high μ road surface. Meanwhile, when the drive control assumes a low μ road surface, the vehicle may not be able to exhibit sufficient turning performance on a high μ road surface. It is therefore conceivable to detect a slipping condition, and change drive control on motors for left and right wheels depending on whether the vehicle is on a high μ road surface or a low μ road surface, and to reduce outputs of the motors when the vehicle is traveling on the low μ road surface.
Suppose that the vehicle is traveling on the low μ road surface, and the outputs of the motors have been reduced to perform control corresponding to the low μ road surface. If control is recovered to control corresponding to a high μ road surface during a process in which the condition of the road surface on which the vehicle is traveling changes from a low μ road surface back to a high μ road surface, the rotation rates of the motors may abruptly increase to cause the vehicle to get into a slipping condition again. If this happens, the slipping condition is detected, and the outputs of the motors are reduced, and accordingly, the control corresponding to the low μ road surface is performed again. Thereafter, during a process in which the condition of the road surface changes from a low μ road surface back to a high μ road surface, the above process is repeated. Thus, the rotation rates of the motors may repeatedly increase and decrease to cause a hunting.
Meanwhile, in order to prevent such a hunting in the motor rotation rates, it is conceivable to prolong a time in which control is recovered to the control corresponding to the high μ road surface for the sake of increased safety in a process in which the condition of the road surface changes from a low μ road surface back to a high μ road surface. This delays a recovery to turn assist control corresponding to the high μ road surface, and may cause a reduction in turning performance of the vehicle.